Even though it is very rare, I have seen some cases on the Discussion forums/Youtube of Muslims converting to Christianity. When I watched these videos there were common reasons among the converts. Some of the top reasons are: 1) Historical data proves that Jesus was crucified/killed and 2) Seeing dreams/visions of signs that is inviting them to the truth/right path (Christianity). These two arguments are valid but if these converts really understood the Quran and Sunnah, then they would have discovered that these arguments are very weak.
Muslims converting to Christianity due to the Christian historical proof that Jesus was crucified is answered in the Quran very clearly: “And [for] their saying, “Indeed, we have killed the Messiah, Jesus, the son of Mary, the messenger of Allah .” And they did not kill him, nor did they crucify him; but [another] was made to resemble him to them. And indeed, those who differ over it are in doubt about it. They have no knowledge of it except the following of assumption. And they did not kill him, for certain.” (Chapter Al-Nisa;a, verse 157). So the Jews actually killed someone else but they thought they killed Jesus and Allah would not allow the murder of His prophet.
So when this is passed down in history (whether it is word of mouth or by writing), they did really think that they killed Jesus and that is why historical studies proves that Jesus was crucified. If the Quran did not reveal what really happened, then no one would have known the truth. Some historians say that the man killed was actually one of Jesus’s disciples who sacrificed himself to ensure the safety of Jesus. In Islam, we believe in dreams and we have evidence for this in the Quran, Sunnah, and in 1000s of cases that happened to the believers of Islam. So I am not doubting that Muslims converting to Christianity have seen dreams, however the question that needs to be asked is how can you confirm that it was real? According to the Sunnah, there are 3 types of dreams: 1) A message/vision given to you by a demon/devil, 2) A message/vision given to you by an Angel with the permission of Allah, 3) A message/vision that is only a hadith al-nafs (a conversation of the soul). A conversation of the soul occurs in most cases and it is usually a reflection of the activities that you are involved with in your daily life. For example, if someone is studying a certain topic such as Christianity and he/she is constantly researching this throughout the days then it is possible that they will see messages/vision related to Christianity in their dreams. A demon coming into your vision and giving you false information to mislead you from the truth is also a known case and that is due to the sins we commit in our lives everyday (No one is perfect). Therefore, Muslims converting to Christianity need to evaluate their dreams/vision and find out if it is really a sign from God or is it only a conversation of the soul or a satanic misleadings. May Allah guide all people to the right path.